1. Field of the Invention
The present invention relates generally to apparatus and processes for the treatment of materials. More specifically, the invention disclosed herein relates to apparatus and processes for processing materials by the exposure thereof to sonic and ultrasonic oscillations.
2. Description of the Prior Art
Sonic and ultrasonic processing devices for the treatment of materials (usually a medium in the liquid phase) are well known in the prior art. Generally, they can be characterized as either static (or batch) processors or continuous, flow-through ultrasonic processors. As will be understood by those skilled in the art, the term "ultrasonic" sometimes is used to refer to frequencies in excess of 20,000 H.sub.z and the term "sonic" sometimes refers to frequencies less than 20,000 H.sub.z. However, for the purpose of the present invention it will be understood that the term "ultrasonic" will be used generally herein to refer to all frequencies. Ultrasonic processors, as that term is used herein, generally refers to devices which can produce, within a material or medium, oscillations at a predetermined frequency, which oscillations are used generally for treatment of the material by processes such as emulsification, solubilizing, cleaning, etc.
Static processors usually comprise a processing chamber for containing the material to be treated and at least one plate or transducer for being oscillated at a predetermined frequency and for oscillating said material.
Continuous, flow-through processors known in the prior art generally comprise a processing chamber through which the material to be processed flows or circulates and at least one transducer for being in contact with the processing chamber or flowing material and for being oscillated at a predetermined frequency.
However, such prior art ultrasonic processors are limited in size and not suitable for use with materials comprising liquid having large solid particles therein such as, for example, a "slurry" or "pulp" of mineral ore mixed with a liquid leaching compound. Thus, prior art ultrasonic processors are unavailable for either high volume processing or for efficient use in extraction of minerals from ores. The essential reason for such unsuitability of prior art devices is their inability to provide large ultrasonic processing chambers. This limitation is a result of the inherent limitations of prior art ultrasonic processors with respect to the manner in which they act upon materials to produce the desired effects.
It is known that the achievement of the desired results by ultrasonic processors is not a gradual process but rather a threshold effect. That is, until a certain power intensity or threshold of ultrasonic oscillations is reached, the desired result is not achieved. The amplitude or intensity at which this effect occurs is called the "threshold level." Increasing the amplitude or intensity of sonic energy substantially above the threshold level does not usually enhance the results to any great degree.
In practice, threshold levels may be fairly easily utilized and achieved in static processors since the cavitation effects, characterized by tremendous differential pressures, can occur within all areas of the material to be processed within two to three inches of the transducer surface in a matter of seconds.
The achievement of threshold effects in continuous flow-through processors is not so easily accomplished in view of the obvious time factor causing the material to be exposed to the ultrasonic oscillations for only a limited period of time (determined by the rate of flow). In continuous flow processing it is necessary to cause the cavitational effects to impinge upon all required sites within the material being processed while insuring that the threshold effect power level is applied to these sites rapidly to enable as high a flow rate as possible.
Certain continuous flow processing apparatus are known in the prior art which minimize this time factor by creating a very small processing volume having a large surface area in contact with the oscillating plates which are separated by an extremely small distance on the order of point 1-25 millimeters. An example of one such prior art device is shown in U.S. Pat. No. 4,071,225, dated Jan. 31, 1978. Such prior art continuous flow processors are obviously less efficient than larger ones and are unsuitable for the processing of large volumes of materials, particularly in the mining or minerals industry where the solid phase particulates exceed the maximum spacing of transducers in these prior art continuous flow processors.
Thus, it is one object of the invention disclosed herein to provide an ultrasonic, continuous flow processor having processing chambers greater in size then prior art processors and where the oscillating plates may, for example, be separated up to the order of magnitude of 120 inches, this spacing being a function of the frequency used in the processor.
Presently, metallic ores are chemically leached to extract the metal therein without the aid of ultrasonic processors. For example, silver and gold ores have been leached with cyanide. However, this process is a function of surface oxidation of the silver and gold. With adequate cleaning of the surfaces of these ores, the productivity of such leaching techniques can be considerably increased. Continual cleaning of the surface as may be effected by ultrasonic processors will produce fresh surface to work with, therefore, an increase in the efficiency of leaching processes will serve to increase ore recoveries and decrease extraction times considerably. Uranium extraction can also be enhanced in this way. Such continual cleaning also enhances dissolution of oxygen in leaching of gold, silver and uranium ores, thus having further beneficial effects as will be apparent to those skilled in the arts. Accordingly, it is a further object of this invention to provide an ultrasonic, continuous flow processor for use in extraction of mineral ores.
Furthermore, prior art ultrasonic processing devices do not incorporate means to vary the frequency, amplitude and/or phase of oscillations produced in oscillating members. While prior art processors such as that disclosed in the aforementioned U.S. Pat. No. 4,071,225 are known to mix frequencies of transducers within one ultrasonic processing device, each transducer used is such device is fixed to oscillate only at one predetermined frequency and with no variation of phase or amplitude among the various transducers. Accordingly, it is another object of this invention to produce means for controlling and effecting frequency, amplitude and/or phase variations in ultrasonic processors.
Heretofore, ultrasonic processor devices have not been capable of optimizing the power drawn into the moving pulp stream in order to better match the operating impedance of the material being processed. This resulted in an inefficient operation of prior art devices. Accordingly, a further object of the invention is to provide means for maximizing an ultrasonic effect within an ultrasonic processor by maximizing power transfer to the material being processed.